Image forming device with misregistration correction achieved by photo-conductor speed controlled variation of latent image tilt

ABSTRACT

As the speed of a photoconductor drum 1a can be independently varied by providing a rotational speed adjustment mechanism to the photoconductor drum 1a, an inclined angle in a diagonal direction can be varied and as a result, misregistration can be adjusted. Also, exposure device with the inclination of a scanning line with the photoconductor drum 1a provided and control over correcting the inclination of the scanning line on the photoconductor drum 1a is executed by control over varying the peripheral speed of the photoconductor drum 1a. Hereby, a multiple image formation device wherein the configuration of color misregistration correction device is simplified is provided as an image formation device used for the output device of a computer and others.

TECHNICAL FIELD

The present invention relates to a multiple image formation devicewherein a synthetic image can be formed by overlapping image informationon transfer material utilizing electrophotography and others.

BACKGROUND ART

Heretofore, in an image formation device adopting electrophotography, anelectrophotographic photoconductor as an image carrier is electrified byan electrifier, a latent image is formed by radiating a beam accordingto image information on the photoconductor, the latent image isdeveloped by a developing machine and the acquired image is transferredon sheet material and an image is formed.

In the meantime, as color printing is demanded, a tandem multiple imageformation device wherein plural image carriers for each image formationprocess are provided, a cyan image, a magenta image, a yellow image,desirably a black image are formed by the respective image carriers anda full color image is formed by overlapping and transferring each colorimage on sheet material in a transfer position of each image carrier isalso proposed.

Such a tandem multiple image formation device is advantageous in speedupbecause each image formation part is provided every color.

However, there is a problem that it is difficult to satisfactorilyregister each image formed by different image formation parts. Thereason is that the misregistration of four color image formationpositions transferred on sheet material finally appears as a irregularcolor or as the change of a color tone.

For the types of the above misregistration of transfer positions, asshown in FIGS. 5(a), 5(b), 5(c) and 5(d), there are misregistration (atop margin) in a write direction (shown by an arrow A in FIG. 5(a)) on ascanning line on a transfer material 9, misregistration (a left margin)in a scanning direction (shown by an arrow B in FIG. 5(b) perpendicularto the direction shown by the arrow A), misregistration in a diagonaldirection shown in FIG. 5(c) and misregistration due to an error ofmagnification shown in FIG. 5(d) and actually, an image in which theabove four types of misregistration is overlapped appears.

The above misregistration is mainly caused by the lag of timing at whicheach image formation station begin to draw an image in the case of a topmargin shown in FIG. 5(a) and by the lag of timing at which each imageformation station draws an image in the case of a left margin shown inFIG. 5(b), that is, the lag of timing for the start of scanning on onescanning line.

The misregistration in a tilt in the diagonal direction shown in FIG.5(c) is caused by misregistration in an angle at which a scanningoptical system is arranged or misregistration in the angle of therotation shaft of a photoconductor drum, and the misregistration due toan error of magnification shown in FIG. 5(d) is caused by difference inthe length of a scanning line due to the error of optical path lengthfrom the scanning optical system of each image formation station to aphotoconductor drum.

To eliminate the above four types of misregistration, first, thequantity of misregistration is corrected by adjusting the scanningtiming of each color as to a top margin shown in FIG. 5(a) and a leftmargin shown in FIG. 5(b). As to the misregistration due to an error ofmagnification and the misregistration in a tilt, the quantity ofmisregistration can be corrected by independently adjusting a pair ofmirrors 101 and 102 the respective mirror faces of which are heldopposite at a right angle out of three folded mirrors 101, 102 and 105arranged on the way of the optical path of each station shown in FIG. 6in directions shown by arrows M and N with the body of the device asshown in FIG. 6 by actuators 103 and 104.

For the actuator for the above adjustment, a linear step actuatorprovided with a step motor which is a driving source for enablinggradual linear movement and others are used.

The above configuration is extremely effective to prevent themisregistration of four colors.

However, according to the above prior configuration, as theconfiguration of correction means for the misregistration due to anerror of magnification shown in FIG. 5(c) and the misregistration in atilt shown in FIG. 5(d) is particularly complicated and many parts arerequired for each correction means, the above prior configuration has adefect that the above correction means is readily vibrated. Therefore,there is a problem that a photoconductor is vibrated in the position ofa laser beam radiated on the photoconductor, it appears as thenonuniformity of scanning, the nonuniformity of scanning appears asdifference in a color tone of an output image and the image isremarkably deteriorated.

The above problem is a very serious problem when an image free of themisregistration of colors and having high quality is to be formed by adigital multicolor image formation device.

The object of the present invention is to provide a multiple imageformation device wherein the configuration of misregistration correctionmeans is simplified, the cost is reduced, further, adjustment formisregistration is facilitated and misregistration in each pixel in caseimages respectively acquired by optical scanning using plural lightbeams are overlapped is eliminated.

DISCLOSURE OF THE INVENTION

According to the present invention for solving the above problems, speedadjustment means for changing the rotational speed of each image carrieris provided and owing to the above configuration, a multiple imageformation device enabling the adjustment of misregistration in a tilt ina diagonal direction can be obtained.

According to another invention of the present invention, exposure meansis arranged so that the exposure means scans a photoconductor with apredetermined tilt to a perpendicular direction to the rotationaldirection of the photoconductor and speed adjustment means for varyingthe rotational speed of each photoconductor is included, owing to theabove configuration, a multiple image formation device wherein thecoefficient of variation of the tilt of an image on transfer material tothe variation of the rotational speed of each photoconductor isincreased, change in rotational speed is minimized and the adjustment ofmisregistration in a tilt in a diagonal direction is enabled isobtained.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing a multiple image formation deviceequivalent to an embodiment of the present invention;

FIG. 2 is a phase diagram showing the correction of misregistration in awrite area on an image carrier of the multiple image formation deviceequivalent to the embodiment of the present invention;

FIG. 3 is a phase diagram showing the correction of misregistration inthe write area on the image carrier of the multiple image formationdevice equivalent to the embodiment of the present invention;

FIG. 4 is a phase diagram showing the correction of misregistration in atransfer belt area of the multiple image formation device equivalent tothe embodiment of the present invention;

FIGS. 5(a) to 5(d) respectively show an error related to the scanningline of a conventional type multiple image formation device; and

FIG. 6 is a perspective view showing the schematic configuration of acompensator of the conventional type multiple image formation device.

A reference number 1a denotes a photoconductor drum, 2a denoteselectrification means, 3 denotes exposure means, 3K denotes a scanningline, 4a denotes developing means, 5a denotes transfer means, 6a denotescleaning means, 7 denotes an intermediate transfer belt, 8 denotes apaper feed roller, 9 denotes sheet material, 11 denotes a sheet materialtransfer roller, 12 denotes fixing means and 13 denotes a driving motor.

PREFERRED EMBODIMENTS OF THE INVENTION First Embodiment

A first embodiment of the present invention will be described below.

The present invention equivalent to the first embodiment relates to amultiple image formation device composed of plural image carriers,plural image formation means for forming an image on each image carrierand speed adjustment means for varying the rotational speed of eachimage carrier forming a synthetic image on transfer material bysequentially overlapping images held on each image carrier on transfermaterial wherein misregistration in a tilt in a diagonal direction canbe adjusted by varying the rotational speed of each image carrier.

FIG. 1 is a block diagram showing the multiple image formation deviceequivalent to the first embodiment of the present invention, FIG. 2 is aphase diagram showing the correction of the misregistration of colors ina write area on the image carrier of the multiple image formation deviceequivalent to the embodiment of the present invention and FIG. 4 is aphase diagram showing the correction of the misregistration of colors ina transfer belt area of the multiple image formation device equivalentto the embodiment of the present invention.

First, as shown in FIG. 1, four image formation stations Pa, Pb, Pc andPd are arranged in the image formation device and each image formationstation Pa, Pb, Pc and Pd is provided with a photoconductor drum 1a, 1b,1c, 1d as an image carrier.

Each dedicated electrification means 2a, 2b, 2c, 2d, each exposure means3 for radiating a light beam according to image information on eachphotoconductor drum 1a, 1b, 1c, 1d, each developing means 4a, 4b, 4c,4d, each transfer means 5a, 5b, 5c, 5d and each cleaning means 6a, 6b,6c, 6d are arranged around each photoconductor drum.

The image formation stations Pa, Pb, Pc and Pd respectively form a blackimage, a cyan image, a magenta image and a yellow image.

In the meantime, an intermediate transfer belt 7 without an end isarranged under the photoconductor drums 1a, 1b, 1c, 1d so that the beltpasses each image formation station Pa, Pb, Pc and Pd and is moved in adirection shown by an arrow A.

In such configuration, first, after a latent image in black componentcolor according to image information is formed on the photoconductordrum 1a by the electrification means 2a of the first image formationstation Pa and well-known electrophotographic process means such as theexposure means 3, the latent image is visualized as a black toner imagewith developing material provided with black toner by the developingmeans 4a and the black toner image is transferred on the intermediatetransfer belt 7 by the transfer mean 5a.

In the meantime, while the black toner image is transferred on theintermediate transfer belt 7, a latent image of cyan component color isformed in the second image formation station Pb, next, a cyan tonerimage is acquired with cyan toner by the developing means 4b, the cyantoner image is transferred on the intermediate transfer belt 7 on whichtransfer by the first image formation station Pa is finished by thetransfer means 5b of the second image formation station Pb and isoverlapped with the black toner image.

As to a magenta toner image and a yellow toner image, image formation isexecuted by the similar method and when the overlap of four color tonerimages on the intermediate transfer belt 7 is finished, the four colortoner images are collectively transferred on sheet material 9 such aspaper fed from a paper supply cartridge 10 via a paper feed roller 8 bya sheet material transfer roller 11, are heated and fixed by fixingmeans 12 and a full color image is acquired on the sheet material 9.

When transfer is finished, residual toner is respectively removed fromthe respective photoconductor drums 1a, 1b, 1c, 1d by cleaning means 6a,6b, 6c, 6d and the photoconductor drums are prepared for the next imageformation.

As described above, in the device provided with plural image formationstations Pa, Pb, Pc and Pd, image information is respectively exposed onthe photoconductor drums 1a, 1b, 1c, 1d rotated in a direction shown byan arrow C in FIG. 1 by each scanning line 3K, 3C, 3M, 3Y of laser beamsradiated from laser beam sources in the exposure means 3 and images indifferent colors are sequentially transferred and overlapped on the samesurface of the said intermediate transfer belt 7 carried in thedirection shown by the arrow A in FIG. 1 after a well-known imageformation process, however, when each transfer image position in theimage formation stations Pa, Pb, Pc and Pd is off its ideal position,the result appears as the misregistration or the overlap of images indifferent colors in the case of a multicolor image. In the case of acolor image, the above result appears as difference in hue and whenmisregistration between transfer image positions is further increased,the result appears as misregistration in color and the quality of animage is remarkably deteriorated.

In this embodiment, to eliminate the four types of misregistrationdescribed in the item of a background art, first, for a top margin and aleft margin, the scanning timing of the scanning lines 3K, 3C, 3M, 3Y iselectrically adjusted as in prior examples and the quantity ofmisregistration is corrected.

For misregistration due to an error of magnification, the video clockrate of the scanning lines 3K, 3C, 3M, 3Y is electrically modulated andthe quantity of misregistration is corrected. Finally, formisregistration in a tilt in a diagonal direction, the quantity ofmisregistration is corrected by the following method. Referring to FIGS.2 and 4, a tilt misregistration (skew) correction system according tothe present invention will be described below.

The photoconductor drum 1a of the first image station Pa is rotated in adirection shown by the arrow C by a driving motor 13 shown in FIG. 2. Onthe surface of the photoconductor drum 1a with the same peripheral speedas the moving speed of the intermediate transfer belt 7, a latent imageline e in black component color of image information with a tiltbeforehand set from a scanning start point D to a scanning end point Ein a direction shown by an arrow H is formed by the scanning line 3K ofa laser beam. When writing is executed from the scanning start point Dto the scanning end point F in case the rotational speed of the drivingmotor 13 is increased and the peripheral speed of the photoconductordrum 1a is faster than the moving speed of the intermediate transferbelt 7, a latent image line f smaller than the latent image line 3 ininclination is formed.

Next, the latent image line f is visualized by the developing means 4aand is transferred on the intermediate transfer belt 7 as shown in FIG.4. However, as the peripheral speed of the photoconductor drum 1a isfaster than the moving speed of the intermediate transfer belt 7, theinclination of a line acquired by visualizing the latent image line f isreduced up to the tilt of a transfer line g on the intermediate transferbelt 7. (A line f' shown in FIG. 4 is a transfer line in case theperipheral speed of the photoconductor drum 1a and the moving speed ofthe intermediate transfer belt 7 are equal.) In the meantime, if therotational speed of the photoconductor drum 1a is slower than the movingspeed of the intermediate transfer belt 7, difference between therespective tilts of a latent image line and a transfer line is enlarged.

Hereinafter, for a cyan image, a magenta image and a yellow image, thetilt of a transfer line is also varied by the similar method, images areformed and toner images in four colors are formed on the intermediatetransfer belt 7.

As described above, the peripheral speed of the photoconductor drums 1a,1b, 1c, 1d is varied so that the tilt of the transfer line of each colorimage is equal by varying the tilt of a transfer line andmisregistration in a tilt is corrected. For example, the peripheralspeed of the other photoconductor drums 1b, 1c, 1d is independentlyvaried so as to equalize the inclination of the transfer line g of theother photoconductor drums with the inclination of the transfer line gof the photoconductor drum 1a, the quantity of misregistration iscorrected by adjusting so that the inclinations are equal and theoverlap of toner images in four colors free of misregistration on theintermediate transfer belt is completed.

If the peripheral speed of the photoconductor drums 1a, 1b, 1c is variedbased upon the moving speed of the intermediate transfer belt 7,difference made by correcting misregistration in a tilt in speed betweenthe intermediate transfer belt 7 and each photoconductor drum 1a, 1b,1c, 1d can be minimized.

In the meantime, if the peripheral speed of the photoconductor drums 1a,1b, 1c, 1d is varied based upon faster speed than the moving speed ofthe intermediate transfer belt 7, tension is applied to the intermediatetransfer belt 7 in a contact part between each photoconductor drum 1a,1b, 1c, 1d and the intermediate transfer belt 7 because eachphotoconductor drum 1a, 1b, 1c, 1d tries to rotate faster than theintermediate transfer belt 7 and the disturbance of an image due to thedeflection of the intermediate transfer belt 7 can be prevented.

Second Embodiment

Next, a second embodiment of the present invention will be described.The second embodiment of the present invention relates to a multipleimage formation device composed of plural photoconductors, exposuremeans for radiating a light beam on each photoconductor to form a latentimage and scanning the above photoconductor with a predetermined tilt toa perpendicular direction to the rotational direction of thephotoconductor, plural developing means for respectively developing alatent image formed on each photoconductor, transfer means fortransferring the image developed by the developing means on transfermaterial and speed adjustment means for varying the rotational speed ofeach photoconductor for sequentially overlapping an image developed oneach photoconductor on the transfer material to form a synthetic image,the coefficient of the variation of the tilt of an image on the transfermaterial to the variation of the rotational speed is increased tominimize the variation of the rotational speed and misregistration in atilt in a diagonal direction can be adjusted by arranging the exposuremeans so that the exposure means scans each photoconductor with apredetermined tilt to a perpendicular direction to the rotationaldirection of the photoconductor and varying the rotational speed of eachphotoconductor.

FIG. 1 is a block diagram showing a multiple image formation deviceequivalent to the second embodiment of the present invention, FIG. 3 isa phase diagram showing the correction of misregistration in color in awrite area on the image carrier of the multiple image formation deviceequivalent to the second embodiment of the present invention and FIG. 4is a phase diagram showing the correction of misregistration in color ina transfer belt area of the multiple image formation device equivalentto the second embodiment of the present invention.

As the configuration of the multiple image formation device shown inFIG. 1 is described above, the description is omitted.

A photoconductor drum 1a of a first image station Pa is rotated in adirection shown by an arrow C by a driving motor 13 as shown in FIG. 3.A latent image line e with a tilt beforehand set from a scanning startpoint D to a scanning end point E in a direction shown by an arrow H inblack component color in image information is formed on the surface ofthe photoconductor drum 1a with the same peripheral speed (rotationalspeed) as the moving speed of the intermediate transfer belt 7 by alaser beam scanning line 3K.

If the rotational speed of the driving motor 13 is increased and theperipheral speed of the photoconductor drum 1ais faster than the movingspeed (the reference speed of the photoconductor drum 1a) of theintermediate transfer belt 7, a latent image line f from the scanningstart point D to the scanning end point F which is smaller ininclination than a latent image line e is formed.

Next, the latent image line f is visualized by developing means 4a andis transferred on the intermediate transfer belt 7 by transfer means 5aas shown in FIG. 4. However, as the peripheral speed of thephotoconductor drum 1a is faster than the moving speed of theintermediate transfer belt 7, the inclination of a line acquired byvisualizing the latent image line f shown in FIG. 3 is reduced up to thetilt of a transfer line g on the intermediate transfer belt 7. (A linef' shown in FIG. 4 shows a transfer line in case the peripheral speed ofthe photoconductor drum 1a and the moving speed of the intermediatetransfer belt 7 are the same.) If the peripheral speed of thephotoconductor drum 1a is slower than the moving speed of theintermediate transfer belt 7, the respective tilts of a latent imageline and a transfer line are enlarged.

In this embodiment, the latent image line e has a tilt to aperpendicular direction to the rotational direction of thephotoconductor drum 1a, however, the reason is that the coefficient ofthe variation of the tilt of the transfer line g on the intermediatetransfer belt 7 to the variation of the peripheral speed of thephotoconductor drum 1a is increased.

Considering that the transfer line g is kept at a right angle with therotational direction of the photoconductor drum 1a even if theperipheral speed of the photoconductor drum 1a is varied in case thelatent image line f is formed in a perpendicular direction to therotational direction of the photoconductor drum 1a as shown in FIG. 3and that as the peripheral speed of the photoconductor drum 1a isvaried, the tilt of the transfer line g varies in case the latent imageline f is formed with a tilt to a perpendicular direction to therotational direction of the photoconductor drum 1a, the reason why thecoefficient of the variation of the tilt becomes large is that thevariation of the tilt of the transfer line g on the intermediatetransfer belt 7 to the variation of the peripheral speed of thephotoconductor drum 1a becomes large as the tilt of the latent imageline f to a perpendicular direction to the rotational direction of thephotoconductor drum 1a becomes larger.

If a line is formed with a tilt as described above, the coefficient ofthe variation of the tilt of an image on the intermediate transfer belt7 to the variation of the peripheral speed of the photoconductor drum 1acan be increased, the variation of the peripheral speed of thephotoconductor drum 1a can be minimized and misregistration in a tilt ina diagonal direction can be adjusted, the adjustment of themisregistration in a tilt is simplified and the cost is reduced, theadjustment of the misregistration in a tilt is further facilitated,misregistration in each pixel in case images acquired by opticalscanning by the exposure means 3 are overlapped is eliminated and a highquality of image free of the deterioration of the image can be obtained.

If the latent image line e is sequentially formed on the surface of thephotoconductor drum 1a from the scanning start point D to the scanningend point E in the direction shown by the arrow H by the exposure means3 as in this embodiment and in a relative position between the exposuremeans 3 and the photoconductor drum 1a, the scanning end point E is onthe downstream side of the scanning start point D in the rotationaldirection of the photoconductor drum 1a, the coefficient of thevariation of the tilt of a scanning line on the intermediate transferbelt 7 to the variation of the peripheral speed of the photoconductordrum 1a becomes larger in case the peripheral speed of thephotoconductor drum 1a is slower than the reference speed of thephotoconductor drum 1a, compared with a case that the peripheral speedis faster.

The above is clear as shown in FIG. 3 because if the peripheral speed ofthe photoconductor drum 1a is faster than the reference speed of thephotoconductor drum 1a, the tilt of the latent image line f is moved ina perpendicular direction to the rotational direction of thephotoconductor drum 1a and that if the peripheral speed of thephotoconductor drum 1a is slower than the reference speed of thephotoconductor drum 1a, the tilt of the latent image line f is moved ina direction distant from a perpendicular direction to the rotationaldirection of the photoconductor drum 1a.

As described above, as the coefficient of the variation of the tilt ofan image on the intermediate transfer belt 7 becomes large in case theperipheral speed of the photoconductor drum 1a is slow, compared with acase that the peripheral speed is fast by arranging the scanning endpoint E on the downstream side of the scanning start point D in therotational direction of the photoconductor drum 1a in a relativeposition between the exposure means 3 and the photoconductor drum 1a andin an area in which the peripheral speed of the photoconductor drum 1ais slower than the reference speed of the photoconductor drum 1a, theperipheral speed of the photoconductor drum 1a is varied,misregistration in a tilt in a diagonal direction can be adjusted in anarea in which the load torque of a driving source for rotating thephotoconductor drum 1a is small and a high quality of image is obtained.

In the meantime, if the latent image line e is formed conversely to thatin this embodiment and in a relative position between the exposure means3 and the photoconductor drum 1a, the scanning end point E is on theupstream side of the scanning start point D in the rotational directionof the photoconductor drum 1a, the coefficient of the variation of thetilt of a scanning line on the intermediate transfer belt 7 to thevariation of the peripheral speed of the photoconductor drum 1a becomeslarger in case the peripheral speed of the photoconductor drum 1a isfaster than the reference speed of the photoconductor drum 1a, comparedwith a case that the peripheral speed is slower.

The reason is that if the peripheral speed of the photoconductor drum 1ais slower than the reference speed of the photoconductor drum 1a, thetilt of the latent image line f is moved in a perpendicular direction tothe rotational direction of the photoconductor drum 1a and if theperipheral speed of the photoconductor drum 1a is faster than thereference speed of the photoconductor drum 1a, the tilt of the latentimage line f is moved in a direction distant from a perpendiculardirection to the rotational direction of the photoconductor drum 1a.

As described above, as the coefficient of the variation of the tilt ofan image on the intermediate transfer belt 7 becomes large by arrangingthe scanning end point E on the upstream side of the scanning startpoint D in the rotational direction of the photoconductor drum 1a in arelative position between the exposure means 3 and the photoconductordrum 1a in case the peripheral speed of the photoconductor drum 1a isfast, compared with a case that the peripheral speed is slow,misregistration in a tilt in a diagonal direction can be adjusted in anarea in which the peripheral speed of the photoconductor drum 1a isfaster than the moving speed at which transfer efficiency is enhanced ofthe intermediate transfer belt 7 and the peripheral speed of thephotoconductor drum 1a is varied in an area in which the peripheralspeed is faster than the moving speed of the intermediate transfer belt7, misregistration in a tilt in a diagonal direction can be adjustedwith tension always applied to the intermediate transfer belt 7 and ahigh quality of image is obtained.

For a cyan image, a magenta image and a yellow image, the images arealso formed by varying the tilt of a transfer line by the similar methodand toner images in four colors are formed on the intermediate transferbelt 7.

As described above, the peripheral speed of each photoconductor drum 1a,1b, 1c, 1d is varied by varying the tilt of a transfer line so that thetilt of each transfer line of color images is equal and misregistrationin a tilt is corrected. For example, the peripheral speed of the otherphotoconductor drums 1b, 1c, 1d is independently varied to match withthe inclination of the transfer line g on the photoconductor drum 1a,the quantity of misregistration is corrected by adjusting so that eachinclination is equal and the overlap of toner images in four colors freeof misregistration in color on the intermediate transfer belt iscompleted.

INDUSTRIAL AVAILABILITY

As described above, according to the present invention, as speedadjustment means for varying the rotational speed of each image carrieris provided, an inclined angle in a diagonal direction can be varied byindependently varying the speed of each image carrier andmisregistration in a tilt in a diagonal direction can be adjusted, theconfiguration of color misregistration correction means can besimplified, the cost can be reduced and further, misregistration incolor can be readily adjusted.

Also, as misregistration in a tilt in a diagonal direction can beadjusted with the coefficient of the variation of the rotational speedof the image carrier to transfer material minimized by varying therotational speed of the image carrier based upon the moving speed of thetransfer material, the disturbance of an image due to friction betweenthe image carrier and the transfer material can be minimized.

Also, as misregistration in a tilt in a diagonal direction can beadjusted with tension always applied to transfer material by varying therotational speed of the image carrier in an area in which the rotationalspeed is faster than the moving speed of the transfer material, thedisturbance of an image due to the deflection of the transfer materialcan be inhibited.

In the meantime, according to the present invention, the coefficient ofthe variation of the tilt of an image on transfer material to thevariation of the rotational speed is increased, the variation of therotational speed is minimized, misregistration in a tilt in a diagonaldirection can be adjusted, the adjustment of misregistration in a tiltis simplified, the cost is reduced, further, misregistration in a tiltcan be readily adjusted, misregistration in each pixel in case imagesoptically scanned by plural exposure means are overlapped is eliminatedand a high quality of image free of the deterioration of the image canbe obtained by arranging the exposure means so that the exposure meansscans the photoconductor with a predetermined tilt in a perpendiculardirection to the rotational direction of the photoconductor, providingspeed adjustment means for varying the rotational speed of therespective photoconductors and varying the rotational speed of eachphotoconductor.

Also, as the exposure means scans by sequentially radiating a light beamin a direction tilted by predetermined quantity in a perpendiculardirection to the rotational speed of the photoconductor, the end pointof scanning is on the downstream side of the start point in therotational direction of the photoconductor in a relative positionbetween the exposure means and the photoconductor, the coefficient ofthe variation of the tilt of an image on transfer material becomes largein case the rotational speed of the photoconductor is slow, comparedwith a case that the rotational speed is fast and the rotational speedof plural photoconductors is varied in an area in which the rotationalspeed of the plural photoconductors is slower than the reference speedof the photoconductor, misregistration in a tilt in a diagonal directioncan be efficiently adjusted in an area in which the load torque of thedriving source for rotating the photoconductor is small and a highquality of image is obtained.

Also, as the exposure means scans by sequentially radiating a light beamin a direction tilted by predetermined quantity in a perpendiculardirection to the rotational speed of the photoconductor, the end pointof scanning is on the upstream side of the start point in the rotationaldirection of the photoconductor in a relative position between theexposure means and the photoconductor, the coefficient of the variationof the tilt of an image on transfer material becomes large in case therotational speed of the photoconductor is fast, compared with a casethat the rotational speed is slow, misregistration in a tilt in adiagonal direction can be adjusted in an area in which the rotationalspeed of the photoconductor is faster than the moving speed at whichtransfer efficiency is enhanced of the transfer material and therotational speed of the plural photoconductors is varied in an area inwhich the rotational speed is faster than the moving speed of thetransfer material, misregistration in a tilt in a diagonal direction canbe adjusted with tension always applied to the transfer material and ahigh quality of image is obtained.

What is claimed is:
 1. A multiple image formation devicecomprising:plural photoconductors; exposure means for radiating a lightbeam on said each photoconductor to form a latent image and scanningsaid photoconductor with a predetermined tilt relative to aperpendicular direction to a rotational direction of saidphotoconductor; plural developing means for respectively developing thelatent image formed on said each photoconductor; transfer means fortransferring the image developed by said developing means on a transfermaterial; and speed adjustment means for varying a rotational speed ofsaid photoconductor so as to adjust the tilt of the latent image,wherein: a synthetic image is formed by sequentially overlapping theimages developed on said each photoconductor on the transfer material.2. A multiple image formation device according to claim 1, wherein:saidexposure means scans by sequentially radiating the light beam in adirection tilted by a predetermined quantity relative to theperpendicular direction to the rotational direction of saidphotoconductor; and in a relative position between said exposure meansand said photoconductor, an end point of scanning is on a downstreamside of a start point in the rotational direction of saidphotoconductor.
 3. A multiple image formation device according to claim1, wherein;said exposure means scans by sequentially radiating the lightbeam in a direction titled by a predetermined quantity relative to theperpendicular direction to the rotational direction of saidphotoconductor; and in a relative position between said exposure meansand said photoconductor, an end point of scanning is on an upstream sideof a start point in the rotational direction of said photoconductor.